QML Text items rendered as blocks - some iOS devices

Currently I can consistently reproduce a text rendering error on specific iOS devices. I am successfully loading multiple fonts from a qrc file and it renders fine on most devices. However on one device we are testing now the font is rendering as blocks. The blocks are the proper shape, size and color, which would indicate to me that the font is properly loaded. It's as if the text is being drawn but each glyph is being drawn with a matching background color. Has anyone else experienced this, or is there a known way of controlling the background transparency of QML Text items?